1. Field of the Invention
This invention relates generally to television picture tubes and, more specifically, to television picture tubes having aperture masks with a plurality of line of sight openings therein with the grade side of the aperture mask located adjacent the phosphor screen.
2. Description of the Prior Art
The prior art concept of color television tubes is old in the art as evidenced by numerous patents thereon. Typical of the prior art color television aperture picture tubes is the Fyler, et al. U.S. Pat. No. 2,690,518 which discloses a glass tube with three electron guns located at the rear of the tube. The electron guns direct a beam of electrons at a television aperture mask or shadow mask which is made of a thin metal sheet. Located adjacent the aperture mask and on the opposite end of the tube is a glass face plate. On the face plate there are groups of three phosphor dots or stripes which comprise the three primary colors, red, blue and green. The aperture mask openings are located with respect to the phosphor dots so that electrons from each gun will strike only the phosphor dot or phosphor stripes associated with the opening in the mask. Because of problems in accurately etching the small holes in an aperture mask, the industry has developed etching procedures that require removing a mass of metal from one surface of the aperture mask. This process in effect provides a thinner section on portions of the mask. Since the section is thinner one can accurately etch smaller openings in the thinned sections of aperture mask as opposed to aperture masks with unthinned sections. In a mask etched in this manner the side where the most metal is removed is denoted as the cone side and the opposite side as the grade side. Because of the resulting geometry of the etched opening the grade side of the mask is positioned toward the electron gun with the cone side toward the phosphor screen.
The various types of aperture masks for use in color television tubes include slot masks having elongated slots which are shown in the Yamada, et al U.S. Pat. No. 3,883,770. Yamada shows a series of elongated slots with a bridge or tie bar located between the slots to provide structural strength for the mask. The bridge or tie bar are located on the grade side of the aperture mask that faces the electron gun with the cone side facing the phosphor screen.
The Roeder prior art U.S. Pat. No. 3,809,945 shows an aperture mask for use having a plurality of additional rows of apertures which are etched partway through on the periphery of the aperture mask to provide an intermediate yield strength to the aperture mask.
Another type of prior art mask is shown in the Tomita U.S. Pat. No. 3,787,939 which shows a two material aperture mask which has been etched from opposite sides. The Tomita patent (FIG. 1) illustrates the operating position of the electron beams emanating through the opening from the grade side of the mask. The configuration of each perforation is in the form of a frustum of a cone with the larger diameter cone being on the side located adjacent the phosphor screen.
A method of laying down the phosphor pattern is shown in the Law U.S. Pat. No. 3,770,434 which uses a coating of materials on opposite sides of the mask.
In the prior art television tubes inventions, particularly those utilizing elongated slots, it has been the standard procedure to mount the aperture mask with the grade side facing the electron gun and the cone side facing the phosphor screen to thereby minimize electron scattering which produces inferior color.
The Suzuki, et al U.S. Pat. No. 3,882,347 shows a television slot mask with elongated slots. Note, FIG. 4 reveals the enlarged or cone side toward the face plate and the grade side toward the electron guns. FIG. 2 shows tie bars or bridges which are located on the ends of the slot with the wider portion of the tie bars facing toward the grade side rather than the cone side.
The present invention comprises improvement to television tubes which comprise a television tube with an aperture located therein having the cone side facing the electron guns and the aperture mask having line of sight openings formed by portions of surfaces on the opposite side of the mask forming the boundaries of the line of sight openings. The resulting television picture tube has greater brightness and color purity than prior art television tubes.